1. Field of the Invention
The present invention relates to adhesive tapes for electronic parts to be used as adhesive tapes for fixing the leadframe, TAB tapes or for adhering between parts around leadframes making up a semiconductor device, e.g., lead pins, semiconductor chip mounted substrates, heat spreader, semiconductors themselves.
2. Description of the Related Art
Conventionally, adhesive tapes for fixing a leadframe, TAB tapes, etc., are used as adhesive tapes for use in the interior of resin-molded type semiconductor devices. For example, the adhesive tapes for fixing a leadframe have been used to fix lead pins of the leadframe in order to enhance the efficiency for producing the leadframe itself and the whole semiconductor assembly stages. In general, a leadframe manufacturer tapes a leadframe, and brings it to a semiconductor manufacturer, at which a semiconductor chip is mounted thereon followed by molding the leadframe with a resin. For this reason, it has been required for the adhesive tapes for fixing the leadframe not only to possess general reliability in a level required for semiconductor and enough processability at the time of taping, but also to possess sufficient adhesive strength at room temperature immediately after taping and heat resistance enough for withstanding thermal process at the stages of assembling semiconductor devices.
Conventionally, the adhesive tapes for use in such an application include adhesive tapes applying on a support film of a polyimide film, etc., an adhesive comprising polyacrylonitrile, polyacrylate or a synthetic rubber resin such as acrylonitrile-butadiene copolymer solely, or modified with any other resin or blended with any other resin to come into a B-stage. Adhesive tapes using heat resisting thermoplastic polyimide resin have been utilized recently.
In recent years, resin-molded type semiconductor devices (semiconductor packages) as shown in FIG. 2 have been developed or produced. In FIG. 2, the device has a construction in which lead pins 3 and metal plane 2 are connected by means of an adhesive layer 6, a semiconductor chip 1 is mounted on the metal plane 2, and together with bonding wires 4 between the semiconductor chip 1 and the lead pins 3, they are molded with a resin 5. In general, unilayer adhesive or both-sided adhesive layer is used as the adhesive layer 6.
In the adhesive layer in the resin-molded type semiconductor devices shown in FIG. 2, the use of an adhesive tape to which a conventional adhesive is applied has the problems that the generated gas stains the lead to cause deterioration of the adhesive strength or causes generation of package crack, because of insufficient heat resistance. It is therefore required to develop adhesives for electronic parts having sufficient heat resistance and reliability and adhesive tapes for electronic parts using them.
The present inventor has solved before the above problems by inventing adhesive tapes using an adhesive containing a polyimide composed of repeating units represented by the below-described formulas (1a) and (2b). (Japanese Patent Application Laid-open Nos. 325533/1996 and 67559/1997).
These adhesive tapes however have various problems. For example, there is a problem of easily causing interfacial separation of the adhesive layer from the heat resistant film in the case that the adhesive layer is formed on the heat resistant film. In particular, the interfacial separation at high humidity and high temperature becomes a serious problems because of causing remarkable deterioration of reliability of semiconductor packages. In the case of an adhesive tape consisting only of an adhesive layer, there is the problem that insulation becomes difficult to assure when the tape is bonded under pressure with heat, because the leadframe is embedded in and pierces the adhesive layer.
In the prior semiconductor devices, the leadframe and the plane previously prepared are bonded under pressure with heat by means of a both-sided adhesive tape which was cut by means of a dies. It is therefore necessary to change the dies for cutting the adhesive tape according to the shapes of the leadframe and the plane.
Japanese Patent Application Laid-open No. 291236/1994 discloses a method of bonding heat radiator to the lead frame in the semi-conductor device with an adhesive tape comprising polyimide adhesive layers having each a different glass transition temperature (Tg). However, there is no detailed description concerning component of the adhesive to be used. Since adhesives having each a different molecular structure, the disclosed semiconductor device has the problem that interfacial separation between or on the adhesive layers is easily caused to result in sufficient adhesion between the adhesive layers and insufficient electric reliability.
The present invention has been made for the purpose of solving such problems in the prior arts. Namely, an object of the present invention is to provide an adhesive tape for electronic parts capable of adhesion at a relatively low temperature, with keeping electrical insulation and having sufficient reliability.